1. Field of the Invention
The present invention relates to a light guide plate for use in a liquid crystal display (LCD) and a method for manufacturing the light guide plate, and particularly to a light guide plate having a simple structure including a light emitting surface configured to converge light.
2. Prior Art
In general, LCDs have two main advantages in comparison with cathode ray tubes (CRTs): LCDs are thin, and have low power consumption. It has been said that LCDs might one day completely replace CRT display devices, and LCDs have aroused great interest in many industries in recent times. In general, an LCD needs a surface light source to provide an even light for a clear display.
A surface light source comprises a light source and a light guide plate. The light source may be a linear light source, or one or more point light sources. The light guide plate has an end face through which light is introduced, and two opposite major faces one of which functions as an emission face. The performance of the surface light source greatly depends on the characteristics of the light guide plate employed therein.
A light guide plate functions to change a direction of propagation of light beams emitted from the light source and introduced into the light guide plate, from a direction roughly parallel to the emission face of the light guide plate to a direction perpendicular to the emission face. That is, the light guide plate effectively changes the linear or point light source(s) into a surface light source, for evenly illuminating a whole display screen of the LCD.
FIG. 5 shows a conventional back light system 100, which comprises a light guide plate 103, a linear light source 101 adjacent the light guide plate 103, a reflector 104, and a brightness enhancing film 105 having a plurality of V-shaped prisms 1051. The reflector 104, the light guide plate 103 and the brightness enhancing film 105 are stacked from bottom to top in that order. The light guide plate 103 has a uniform thickness, and comprises an incident surface 1031, an emitting surface 1033, and a bottom surface 1032 opposite to the emitting surface 1033. A plurality of scattering dots 1034 is formed on the bottom surface 1032. The linear light source 101 is covered by a light source cover 102 on three sides thereof, for reflecting light beams into the light guide plate 103. The linear light source 101 is positioned adjacent the incident surface 1031 of the light guide plate 103, and emits light beams into the light guide plate 103 through the incident surface 1031. Light beams thus introduced into the light guide plate 103 are reflected to the brightness enhancing film 105 by the bottom surface 1032. The brightness enhancing film 105 converges the light beams and introduces the converged light beams into an LCD (not shown). The back light system 100 employs a plurality of optical elements and has a plurality of optical interfaces. The various optical interfaces cumulatively contribute to an unduly high loss of light intensity in the back light system 100. That is, the back light system 100 does not attain very effective optical utilization. Moreover, the brightness enhancing film 105 is generally expensive, and inflates the costs of the back light system 100 proportionately.
FIG. 6 shows another conventional back light system 200, which comprises a light source 201, a light guide plate 203, and a light source cover 202 covering three sides of the light source 201. A plurality of V-shaped prisms 2032 is formed on an emitting surface 2031 of the light guide plate 203. A cross-section of each prism 2032 is shaped like an isosceles triangle. The triangle has a vertex angle between 60 and 120 degrees, preferably 90 degrees. The light guide plate 203 further comprises a bottom surface 2033, on which a plurality of scattering dots (not shown) is formed. In operation, light beams from the light source 201 are introduced into the light guide plate 203, and then reflected and scattered by the scattering dots on the bottom surface 2033 in directions toward the emitting surface 2031.
In the back light system 200, the prisms 2032 of the emitting surface 2031 are integrated with the light guide plate 203. The luminance of the light guide plate 203 is mainly determined by the vertex angle of the prisms 2032 and the smoothness of the surfaces of the prisms 2032. To assure good luminance of the light guide plate 203, a high precision mold with tolerances of only 1 to 2 micrometers is needed for manufacturing the light guide plate 203. Generally, this kind of mold takes seven days to make. This long period operates to increase the cost of the light guide plate.
A new light guide plate that overcomes the above-mentioned disadvantages is desired.